Want to know the future of California weather? You might want to ask the coral in Kiribati, an island nation in the central tropical Pacific Ocean. Jessica Carilli, assistant professor of coastal geochemistry in the School for the Environment at UMass Boston, is the lead author of a new paper in Paleoceanography that reveals how the tropical Pacific climate has changed to increase the chance of El Niño conditions in the future. Carilli uses coral to learn about climate conditions in the Pacific.

Trade winds (a part of what is known as the Walker Circulation) in the western Pacific are crucial to the “normal” weather patterns that we are accustomed to seeing across the western hemisphere. As our oceans warm, those trade winds may break down and cause what Carilli calls “El Niño-like conditions,” that in turn could allow true El Niño events to develop more readily. El Niño is an irregularly occurring, large-scale climate event that results in altered weather patterns. During a typical El Niño, Indonesia experiences intense drought, while California receives a dramatic increase in rainfall.

According to Carilli, coral act as a “natural archive.” Scientists can extract small core samples from coral and examine the chemical makeup of its growth bands (just like the rings of a tree) to learn about the environment that surrounded the coral as it grew, including salinity and temperature of the water. Since the coral core from the Gilbert Islands in the Republic of Kiribati lived for almost 60 years, the scientists now have a detailed, decades-long record of the climate in this part of the Pacific. The Kiribati coral indicates that, over the past half-century, average conditions have changed, and the Pacific is primed for El Niño events.

Carilli warns that changes in these average Pacific conditions can lead to larger climatic change. “Historically, El Niño events occurred every two to seven years. But as the climate state changes, trade winds get weaker, meaning that El Niño events could become more common or intense, which is not great for many regions, or for global temperatures.”

Working with colleagues in the United States, Australia, and Canada, Carilli is contributing to a network of coral records throughout the Pacific that scientists can use to examine the climate of the region over time.